1. Field of the Invention
The present invention relates to a displacement compressor used for compressing the refrigerant of an automotive air-conditioning system, or in particular to a scroll-type compressor.
2. Description of the Related Art
In an air-conditioning system of an automotive vehicle, for example, the need for an inexpensive, compact and lightweight refrigerant compressor and the fact that the electromagnetic clutch normally provided for transmitting or cutting off the driving force from an engine is expensive, bulky and heavy have led to the demand for a compressor of new type which requires no electromagnetic clutch. To meet this demand, a swash plate compressor has already been practically used, in which the discharge capacity can be changed from 100% to 0% by changing the inclination of the swash plate. However, a scroll-type compressor of which the discharge capacity can be reduced to 0% has yet to be realized.
For eliminating the electromagnetic clutch added to the scroll-type compressor, it is necessary that the scroll-type compressor can operate with 0% capacity to reduce the discharge capacity thereof to zero in substantially the same manner as if the electromagnetic clutch is off on the one hand and that the power loss in operation is so small as to have no adverse effect on the fuel cost of the automotive vehicle on the other.
To cope with this problem, the variable-capacity type refrigerant compressor of a scroll type described in Japanese Unexamined Patent Publication No. 5-231353 has been proposed in the prior art. In this compressor, a bypass is arranged between a compression chamber formed between a stationary scroll member and a movable scroll member and an intake chamber on the low-pressure side, and the discharge capacity is changed by opening/closing the bypass with a shuttle valve or the like. Since the compressed refrigerant cannot be fully returned to the intake chamber when the compressor is operating at high speed, however, it is difficult to achieve 0% capacity.
In what is called a combination system, having both a bypass from the compression chamber and a bypass from the discharge chamber where the compressed refrigerant is concentrated such as the scroll-type compressor described in Japanese Unexamined Patent Publication No. 4-179887, the following problem is posed. Specifically, in the operation at 0% capacity, the entire amount of the refrigerant compressed is returned from the discharge chamber to the intake chamber and the orbiting radius of the movable scroll member is constant, so that the operation of 0% capacity remains the same as with that of 100% capacity. Therefore, the friction of the sliding parts is as large for 0% capacity as for 100% capacity, and the power loss in the 0% capacity operation is increased to a not-negligible degree.
Further, in the scroll-type compressor described in Japanese Unexamined Patent Publication No. 2-252990, not only the movable scroll member is moved but also the stationary scroll member is rotated relatively to the movable scroll member, and the crankshaft radius is made variable to assure smooth contact between the movable scroll member and the stationary scroll member. The mechanism in which the stationary scroll member is rotated as well as the movable scroll member, however, poses the problem that the structure is complicated and the compressor becomes bulky as a whole.
The object of the present invention is to obviate the aforementioned problem of the prior art, using a novel means, and to provide a compact, lightweight and inexpensive scroll-type compressor in which not only the electromagnetic clutch is eliminated but also the power loss is minimized in the 0% capacity operation by realizing the complete 0% capacity operation.
According to the invention, as a means for solving the problem described above, there is provided a scroll-type compressor comprising a housing journaling a drive shaft, a stationary scroll member including an end plate fixed on the housing and a spiral blade around the center axis of the shaft, a movable scroll member including an end plate and a spiral blade forming a plurality of compression chambers by engaging the spiral blade and the end plate of the stationary scroll member, the movable scroll member being capable of orbiting around the center axis of the shaft, a compliance crankshaft mechanism interposed between the shaft and the movable scroll member for orbiting the movable scroll member by the shaft and allowing the orbiting radius of the movable scroll member to change steplessly downward substantially to zero, a guide hole formed in a selected one of the movable scroll member and the housing and having an inclined surface with the depth along the center axis of the shaft changing in a radial direction, a plunger supported on a selected one of the movable scroll member and the housing in which the guide hole is not formed and which is adapted to advance toward and retract from the guide hole to thereby assume a selected one of a position in engagement with the guide hole and a position out of engagement with the guide hole, and control operation means for controlling the plunger to advance and retract along the center axis of the shaft.
A scroll-type compressor according to the invention comprises a compliance crankshaft mechanism interposed between a shaft and a movable scroll member for allowing the orbiting radius of the movable scroll member to be reduced steplessly substantially to zero, wherein one of the movable scroll member and the housing is formed with a guide hole, wherein the guide hole has an axis and a conical surface, wherein the axis of the guide hole is parallel to the center axis of the shaft. The other one of the movable scroll member and the housing not formed with the guide hole supports a plunger adapted to move toward and away from the guide hole to select a position to engage or not to engage the guide hole. The plunger is controlled by control means to advance and retract with respect to the direction of the center axis of the shaft.
When the plunger is advanced to the bottom portion of the guide hole, the position of the forward end of the plunger engaging the inclined surface of the guide hole so changes that the engagement changes to a higher position of the inclined surface. Thus, the movable scroll member is pushed down radially, and the center of the movable scroll member approaches and finally comes to coincide with the center of the stationary scroll member. In this condition, the compression chamber formed between the spiral blade of the movable scroll member and the spiral blade of the stationary scroll member is open, and therefore the fluid like the refrigerant is not compressed. Thus, the operation capacity is reduced to 0%, and even when the shaft is in rotation, the discharge amount is reduced substantially to zero. Under this operating condition, the compressor substantially fails to work, and therefore the power consumption is reduced substantially to zero even when the shaft is in rotation. Thus, the same condition is developed as if the electromagnetic clutch is deenergized.
In another embodiment, a guide hole can alternatively be formed in the end plate of the movable scroll member, and the plunger is supported by the housing. Conversely, a guide hole may be formed in the plunger adapted to move by being supported on the housing, and a pin engaging the guide hole may be arranged on the end plate of the movable scroll member as another alternative. As still another alternative, a guide hole is formed in the eccentric bushing of the compliance crankshaft mechanism supporting the end plate of the movable scroll member, while at the same time supporting the plunger on the shaft journaled by the housing.
A guide hole configured of a two-stepped conical surface can be reduced in depth. In the case where the guide hole is formed of a curved surface such as a quadratic surface of revolution, on the other hand, the same effect can be achieved smoothly as the two-stepped conical surface. Provision of energization means such as a spring for retreating the plunger completely from the position of engagement with the guide hole can always realize the operation of 100% capacity. Nevertheless, the configuration can be simplified by omitting the energization means. Also, if the edge portion of the guide hole opening is formed with a cylindrical surface, on the other hand, the rotation of the movable scroll member can be prevented by use of the guide hole, and therefore the need of an antirotation mechanism is eliminated.
One or several plungers may be provided. In the case where a single annular plunger is arranged in such a position as to surround the centerline of the shaft, the axial force can be generated against the guide hole uniformly around the shaft. Thus, the movable scroll member can be smoothly operated in radial direction, thereby making it possible to prevent vibration or the like.
If a counter weight is mounted radially movably on the shaft with a bifacial portion, while the movable scroll member is moved radially in such a manner as to reduce the discharge capacity to zero, the counter weight that has thus far been in contact with the outer periphery of an eccentric bushing constituting a part of the compliance crankshaft mechanism comes into contact with the outer periphery of a large-diameter boss portion constituting a part of the shaft while leaving the outer periphery of the eccentric bushing from a predetermined time point. By configuring in this way, an excessively large pressure is prevented from being imparted between a pair of the spiral blades forming the compression chamber by the large centrifugal force exerted on the movable scroll member under a heavy-load, high-speed operating condition. In this way, the wear of the spiral blades can be suppressed.
Further, in the case where a bypass adapted to establish communication between the compression chamber of intermediate pressure in the process of compression and the lower pressure side is opened to the end plate of the stationary scroll member and control means is provided for opening/closing the bypass, the compression chamber of intermediate pressure communicates with the low-pressure side when the bypass is opened by the control means. As a result, the discharge capacity is reduced, so that an intermediate discharge capacity between 100% and 0% can be achieved in stable fashion. In this way, the discharge capacity can be selectively controlled in three stages very easily.
As described above, with the scroll-type compressor according to this invention, the operation of 0% capacity with a very small power loss can be realized by reducing the orbiting radius of the movable scroll member to zero. Therefore, a scroll-type compressor with a variable discharge capacity free of the electromagnetic clutch can be provided.